While previous research has recognized the importance of strategic alliances in the general business context, little is known about how they relate to environmental improvement, in spite of their increased business use in this arena. This study integrates resource-based view or institutional theory to assess variations in firm-level motivations to form strategic alliances that address complex environmental issues. It proposes that strategic alliances typically are either competency- or legitimacy oriented, and that three structural configurations characterize both types of alliances—organization learning, partner diversity, and governance structure. These configuration variances in turn influence firms’ likelihood to pursue more (or less) proactive environmental strategies. This model is tested empirically for a sample of 74 firms that participated in 146 environmental alliances. Results suggest that firms participating in competency-oriented alliances are more likely to conduct exploration learning, have diverse partners and adopt non-equity governance structure, which in turn may associate firms with more proactive environmental strategies.